Persoonia and the origin of the Australian flora
Australian vegetation is now dominated by a large, central arid zone that separates several marginal 'islands' of more mesic biomes (including sclerophyll forests, sclerophyll woodlands and heathlands). The origins of this pattern remain controversial. Two competing hypotheses have been proposed to account for the origin of the arid biome. One hypothesis postulates that this diversity was derived by repeated colonisation events from the mesic areas, and predicts repeated sister relationships between mesic and arid areas. The other holds that the arid vegetation evolved in situ as the Tertiary rainforests contracted and the continent dried out resulting in arid groups in a particular genus or family that are related as a single lineage. The evidence is sparse and conflicting. Geological evidence for arid zone groups is also equivocal; fossil microfloras from central Australia have highly variable assemblages. It has been inferred that these microfloras reflect earlier occurrences of plant groups indicative of dry conditions (e.g. Eucalyptus). Evidence for the age of the arid zone is problematic. Competing hypotheses also seek to explain the history of fragmentation of the mesic biomes, either as a result of inundation by Cretaceous epicontinental seas or later Tertiary aridification.
Diversification in the Proteaceae largely pre-dates geological evidence for the existence of the arid zone but mostly post-dates Cretaceous inundation. Therefore, the family is an ideal model group to test these evolutionary hypotheses. By integrating molecular phylogenetic techniques with pollen data (both fossil and living) we will contribute substantially to resolving the likely origins of the mesic and arid zone biotas. Our research targets the genus Persoonia (Proteaceae). The distribution pattern of Persoonia is seen in many other larger Australian genera (e.g. Banksia-Dryandra, Hakea and Grevillea). Although some of these genera extended further into the arid zone, targeting a group with multiple arid-mesic relationships will best test our invasion versus in situ origins hypotheses.
Similar distributions and patterns of diversity may be the result of similar processes, and by studying a tractable group, in terms of species numbers, we will be better able to understand current diversity patterns in other distinctive elements of the Australian flora.
- David Cantrill (Royal Botanic Gardens Victoria)
- Daniel Murphy (Royal Botanic Gardens Victoria)
- Peter Weston (Royal Botanic Gardens Sydney)
- Gareth Holmes (Royal Botanic Gardens Victoria)
- Stuart Gardner (Royal Botanic Gardens Victoria, 2010–2012)
- Hermon Slade Foundation